1. Field of the Invention
Embodiments of the present invention relate to the field of stereo audio amplifiers with automatic gain control functions. More particularly, embodiments of the present invention relate generally to a comparator that compares a programmable offset voltage to an audio input for power control of a device.
2. Related Art
As the components required to build a electronic devices have reduced in size, new categories of electronic devices have emerged. One of the new categories of electronic devices is the portable electronic device. A portable electronic device is small enough to be used in a mobile environment. That is, the device can be carried about and used conveniently. For example, portable electronic devices include palmtop computer system, cell phones, handheld gaming systems, etc. Some of these portable electronic devices include listening devices that output an audio signal for listening.
Portable listening devices require the efficient use of power in order to extend usable lifetime of a charge on a battery. Unfortunately, portable listening devices including stereo audio amplifiers with automatic gain control consume a great amount of power. This power is consumed by a number of circuits, including operational amplifiers, comparators, analog-to-digital converters, volume control circuit, etc. This power continues to be consumed even if an audio signal is not being generated. As a result, unnecessary usage of battery power leads to shorter usable lifetimes for a charge on a battery used in portable listening devices.
One prior art solution required that parts of the portable listening device be shut down when an audio signal was not detected. While this method did extend the lifetime of a usage of battery power, the resulting powering-up of the device required a long startup period. That is, typically 70 milliseconds (70 ms) would be required before power is restored to the device.
Furthermore, the power-up of those parts of the portable listening device typically required some input by the user. For instance, the user would have to initiate a signal to be generated that would power up those parts of the portable listening device to amplify a audio input signal.
As such, there is a need for a programmable threshold detector that is capable of controlling power when an audio signal is not present for efficient use of power in a portable electronic device.